all: gracefully handle shaky network

Author: sbinet

cached_table.go

@@ -0,0 +1,49 @@
+// Copyright ©2016 The ji-web-display Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+package main
+
+import (
+	"encoding/base64"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+)
+
+func main() {
+
+	id := flag.Int("id", 12779, "timetable ID")
+	host := flag.String("host", "indico.in2p3.fr", "Indico server")
+
+	flag.Parse()
+
+	url := fmt.Sprintf(
+		"https://%s/export/timetable/%d.json?pretty=yes",
+		*host, *id,
+	)
+
+	resp, err := http.Get(url)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer resp.Body.Close()
+
+	w := base64.NewEncoder(base64.StdEncoding, os.Stdout)
+	defer w.Close()
+
+	_, err = io.Copy(w, resp.Body)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	err = w.Close()
+	if err != nil {
+		log.Fatal(err)
+	}
+}

fetch_timetable.go

@@ -7,6 +7,7 @@ package indico
 import (
 	"encoding/json"
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"strconv"
 	"time"
@@ -178,26 +179,39 @@ func FetchTimeTable(host string, evtid int) (*TimeTable, error) {
 	}
 	defer resp.Body.Close()
 
-	var raw timetableResponse
-	err = json.NewDecoder(resp.Body).Decode(&raw)
+	buf, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+
+	tbl := TimeTable{ID: evtid}
+	err = json.Unmarshal(buf, &tbl)
 	if err != nil {
 		return nil, err
 	}
 
+	return &tbl, err
+}
+
+func (tbl *TimeTable) UnmarshalJSON(data []byte) error {
+	var raw timetableResponse
+	err := json.Unmarshal(data, &raw)
+	if err != nil {
+		return err
+	}
+
 	if !raw.Complete {
-		return nil, fmt.Errorf("indico: incomplete timetable")
+		return fmt.Errorf("indico: incomplete timetable")
 	}
 
+	evtid := tbl.ID
 	mdays, ok := raw.Results[strconv.Itoa(evtid)]
 	if !ok || len(mdays) == 0 {
-		return nil, fmt.Errorf("indico: no event with id=%d", evtid)
+		return fmt.Errorf("indico: no event with id=%d", evtid)
 	}
 
-	tbl := &TimeTable{
-		ID:   evtid,
-		URL:  raw.URL,
-		Days: make([]Day, 0, len(mdays)),
-	}
+	tbl.URL = raw.URL
+	tbl.Days = make([]Day, 0, len(mdays))
 
 	for k, mday := range mdays {
 		day := Day{
@@ -207,7 +221,7 @@ func FetchTimeTable(host string, evtid int) (*TimeTable, error) {
 			var session Session
 			err = json.Unmarshal(msession, &session)
 			if err != nil {
-				return nil, err
+				return err
 			}
 			session.sanitize()
 			day.Sessions = append(day.Sessions, session)
@@ -218,10 +232,10 @@ func FetchTimeTable(host string, evtid int) (*TimeTable, error) {
 		}
 		day.Date, err = time.ParseInLocation("20060102", k, loc)
 		if err != nil {
-			return nil, err
+			return err
 		}
 		tbl.Days = append(tbl.Days, day)
 	}
 
-	return tbl, nil
+	return nil
 }

indico/indico.go

@@ -64,20 +64,21 @@ func main() {
 		host = getHostIP()
 	}
 
+	var tbl *indico.TimeTable
+
 	_, err = net.LookupIP("indico.in2p3.fr")
 	if err != nil {
 		log.Printf("error looking up 'indico.in2p3.fr': %v\n", err)
-		log.Printf("sleeping for 5s...\n")
-		time.Sleep(5 * time.Second)
-		_, err = net.LookupIP("indico.in2p3.fr")
+		log.Printf("loading cached table...\n")
+		tbl, err = loadCachedTable(*evtid)
+		if err != nil {
+			log.Fatal(err)
+		}
+	} else {
+		tbl, err = indico.FetchTimeTable("indico.in2p3.fr", *evtid)
 		if err != nil {
 			log.Fatal(err)
 		}
-	}
-
-	tbl, err := indico.FetchTimeTable("indico.in2p3.fr", *evtid)
-	if err != nil {
-		log.Fatal(err)
 	}
 	sortTimeTable(tbl)